FIELD OF THE INVENTION
The invention relates to a further development of a sheet guiding cylinder described in German Patent 42 23 839. A particular use for this sheet guiding cylinder of the German patent is in a chain delivery of a sheet-fed rotary printing press, wherein the sheet guiding cylinder directly follows an impression cylinder. In this regard, the sheet guiding cylinder is located between two chain or sprocket wheels which are concentric to or coaxial with the axis of rotation thereof. A pair of endless delivery chains are slung around the chain wheels and convey, out of the region of the impression cylinder to a sheet pile stacking device, gripper systems carried by the delivery chains, together with sheets coming from the impression cylinder and clamped by the gripper systems. It is thus a task of the sheet guiding cylinder to guide a sheet, respectively, clamped in a gripper system along a conveying path defined by the chain wheels, in such a manner that the print quality of a freshly printed surface facing the sheet guiding cylinder is not diminished by so-called smudging or smearing.
Moreover, the aforementioned heretofore known sheet guiding cylinder is provided with an air cushion for supporting the respective sheet and keeping it away from the outer cylindrical surface of the sheet guiding cylinder during operation. This air cushion is formed by an air flow emerging from a vane ring. The vanes of the vane ring have a curved profile. Thus, one may expect from the aforementioned sheet guiding cylinder of the German patent that, when the formation or design of the curves of the vane profile are advantageous in air flow technology, a favorable relationship between the power supplied to the drive of the vane ring, on the one hand, and the kinetic energy inherent in the air flow emerging from the vane ring, on the other hand, can be achieved. Such an optimization in air flow technology, however, does not generally ensure that a respective sheet will be kept reliably away from the outer cylindrical surface of the sheet guiding cylinder. Operational conditions may arise wherein an opposite effect may occur, namely, a sheet may be pressed against the outer cylindrical surface of the sheet guiding cylinder due to a reduced static pressure created in the vicinity of the sheet and the sheet guiding cylinder due to the effect of air flow emerging from the vane ring. Such operational conditions can be caused, for example, by a change in the mechanical properties of the sheets and by a deviation of the speeds of travel of the sheets from the production speed.